The present invention relates to improvements in ball-and-socket joints in general, and more particularly to improvements in the sockets of such joints. Still more particularly, the invention relates to improvements in the heads as well as to improvements in the shanks or stems of such joints.
It is already known to make the socket of a ball-and-socket joint of a single piece of plastic material. Reference may be had, for example, to German Offenlegungsschrift No. 31 19 061 which discloses a one-piece socket including a head defining a spherical cavity and a shank which can be connected to a motion transmitting or motion receiving part. The head is formed with a slot which divides it into two halves and such halves are movable relative to each other in order to provide room for insertion of a ball into or for its extraction from the spherical cavity. In other words, at least one of the halves must yield during insertion or withdrawal of the ball in order to provide sufficient room for introduction of the ball into or for its removal from the spherical cavity. The joint which is disclosed in the German Offenlegungsschrift further comprises a locking or closing device which is applied to the two halves of the head subsequent to introduction of the ball into its cavity in order to prevent accidental extraction of the head.
The making (e.g., extrusion or injection molding) of such plastic articles is a complex and expensive operation. Thus, the mold must be provided with a suitable insert which causes the formation of the aforementioned slot between the two halves of the head, and the removal of the insert upon completion of the injection molding or extruding operation is a time-consuming procedure which contributes significantly to the overall cost of the finished article. The cost of the mold is rather high, primarily due to the need for an insert which is to ensure the formation of a slot between the two halves of the head.